Timing based approach for efficient switched mode power conversion

Abstract

A DC-DC converter includes a plurality of switches configured to be in a first charging mode until current through an inductor reaches a first current threshold to thereby indicate an end of the first charging mode. Responsive to the end of the first charging mode the DC-DC converter is configured to operate in a second charging mode for a time period ΔT in which a first side of the inductor is coupled to an input voltage and a second side of the inductor is coupled to a load. Responsive to the end of the time period ΔT, the DC-DC converter operates in a discharge mode until current through the inductor reaches its minimum.

What is claimed is: 
     
       1. A method for operating a voltage converter comprising:
 operating the voltage converter in a first charging mode until current through an inductor reaches a first current threshold; 
 after the first charging mode, changing to operate the voltage converter in an intermediate charging mode, in which current is supplied to a load until an end of a time period; 
 in response to the end of the time period operating the voltage converter in a third charging mode, the third charging mode being a discharge mode; 
 in a timing control loop,
 comparing an output voltage of the voltage converter to a ripple voltage reference and supplying a first comparison indication; 
 determining the time period for operating in the intermediate charging mode based on the first comparison indication; 
 
 in a frequency control loop,
 comparing a reference voltage to the output voltage and supplying a second comparison indication; 
 determining a pulse frequency modulation (PFM) frequency of the voltage converter based in part on the second comparison indication and based in part on the time period determined in the timing control loop. 
 
 
     
     
       2. The method as recited in  claim 1 , wherein operating the voltage converter in the first charging mode comprises:
 coupling a first side of the inductor to an input voltage and a second side of the inductor to a second voltage. 
 
     
     
       3. The method as recited in  claim 2 , wherein operating the voltage converter in the intermediate charging mode comprises:
 coupling the first side of the inductor to the input voltage and the second side of the inductor to the load. 
 
     
     
       4. The method as recited in  claim 1 , wherein operating the voltage converter in a first charging mode comprises:
 coupling the first side of the inductor to an input voltage and a second side of the inductor to the load. 
 
     
     
       5. The method as recited in  claim 4 , wherein operating the voltage converter in the intermediate charging mode comprises:
 coupling the first side of the inductor to the input voltage and the second side of the inductor to the load. 
 
     
     
       6. The method as recited in  claim 3 , wherein the current through the inductor is increasing during the intermediate charging mode. 
     
     
       7. The method as recited in  claim 3 , wherein the current through the inductor is decreasing during the intermediate charging mode. 
     
     
       8. The method as recited in  claim 2 , wherein operating in the discharge mode comprises:
 coupling the first side of the inductor to the second voltage and the second side of the inductor to the load. 
 
     
     
       9. A voltage converter comprising:
 an inductor; 
 a control logic; 
 a plurality of switches configurable by the control logic to place the voltage converter in a first charging mode, until a current through the inductor reaches a first current threshold; 
 wherein the control logic is responsive to the current through the inductor reaching the first current threshold to configure the switches to cause the voltage converter to operate in a second charging mode in which a first side of the inductor is coupled to an input voltage and a second side of the inductor is coupled to a load; 
 a compare logic configured to compare an elapsed time in the second charging mode to a time threshold to determine an end of the second charging mode; and 
 wherein responsive to the end of the second charging mode, the control logic configures the switches to operate the voltage converter in a discharge mode in which the first side of the inductor is coupled to a ground node and the second side of the inductor is coupled to the load; 
 wherein the control logic includes,
 a timing control loop configured to determine the time threshold for operating in the second mode based on a comparison of an output voltage of the voltage converter to a ripple voltage reference, the ripple voltage reference formed from a reference voltage and a maximum desired ripple voltage, the timing control loop including a comparator to perform the comparison of the output voltage to the ripple voltage reference; and 
 a frequency control loop configured to compare the reference voltage to the output voltage and supply a comparison indication, the frequency control loop further configured to determine a pulse frequency modulation (PFM) frequency of the voltage converter based in part on the comparison indication and based in part on the time threshold. 
 
 
     
     
       10. The voltage converter as recited in  claim 9 , wherein in the first charging mode the first side of the inductor is coupled to the input voltage and the second side of the inductor is coupled to the ground node. 
     
     
       11. The voltage converter as recited in  claim 9 , wherein in the first charging mode of the first side of the inductor is coupled to the input voltage and the second side of the inductor is coupled to the load. 
     
     
       12. The voltage converter as recited in  claim 9 , wherein the current through the inductor is increasing during the second charging mode. 
     
     
       13. The voltage converter as recited in  claim 9 , wherein the current through the inductor is decreasing during the second charging mode. 
     
     
       14. A DC-DC converter comprising:
 a plurality of switches configured to be in a first charging mode, until current through an inductor reaches a first current threshold to thereby indicate an end of the first charging mode; 
 wherein responsive to the end of the first charging mode the plurality of switches are configured to cause the DC-DC converter to operate in a second charging mode for a time period in which a first side of the inductor is coupled to an input voltage and a second side of the inductor is coupled to a load; and 
 wherein responsive to an end of the time period, the plurality of switches are configured to cause the DC-DC converter to operate in a discharge mode; 
 control logic configured to configure the plurality of switches, the control logic including,
 a timing control loop configured to determine the time period for operating in the second charging mode based on a comparison of an output voltage of the DC-DC converter to a ripple voltage reference, the timing control loop including a comparator to perform the comparison of the output voltage to the ripple voltage reference; and 
 a frequency control loop configured to compare a reference voltage with the output voltage and supply a comparison indication, the frequency control loop further configured to determine a pulse frequency modulation (PFM) frequency of the DC-DC converter based in part on the comparison indication and based in part on the time period. 
 
 
     
     
       15. The method as recited in  claim 1  further comprising:
 forming the ripple voltage reference by adding a maximum desired ripple voltage to the reference voltage. 
 
     
     
       16. The DC-DC converter as recited in  claim 14  wherein the ripple voltage reference differs from the reference voltage by a maximum desired ripple voltage.